Surface Polymerization and Controlled Pyrolysis: Tailorable Synthesis of Bumpy Hollow Carbon Spheres for Energy Storage.

Architectural design of hollow carbon spheres (HCSs) plays a vital role in improving their performance and expanding applications. The tailorable synthesis of bumpy or asymmetric HCSs with a refined structure remains a challenge. Herein, bumpy HCSs (BHCSs) and bumpy concave HCSs (BCHCSs) have been engineered. The synthesis involves the formation of a core/shell precursor via the surface polymerization of pyrrole monomers on polystyrene nanoparticles, followed by the controlled pyrolysis process under different conditions. In comparison with HCSs, the concave hollow structure can reduce the excessive interior cavity and maintain prevalent merits of hollow structures; the bumpy shell can improve the surface area and number of active sites, thus improving the kinetics as energy storage devices. As a result, among BCHCSs, BHCSs, and HCSs, BCHCSs exhibit optimal electrochemical performance. The lithium-ion hybrid capacitors employing BCHCSs as an anode can deliver an energy density of 0.2182 kW h kg-1 at a power density of 0.2235 kW kg-1. Overall, this study provides an innovative design and strategy for constructing unique carbon nano-architectures for energy storage.

Exploring High Aspect Ratio Gold Nanotubes as Cytosolic Agents: Structural Engineering and Uptake into Mesothelioma Cells.

The generation of effective and safe nanoagents for biological applications requires their physicochemical characteristics to be tunable, and their cellular interactions to be well characterized. Here, the controlled synthesis is developed for preparing high-aspect ratio gold nanotubes (AuNTs) with tailorable wall thickness, microstructure, composition, and optical characteristics. The modulation of optical properties generates AuNTs with strong near infrared absorption. Surface modification enhances dispersibility of AuNTs in aqueous media and results in low cytotoxicity. The uptake and trafficking of these AuNTs by primary mesothelioma cells demonstrate their accumulation in a perinuclear distribution where they are confined initially in membrane-bound vesicles from which they ultimately escape to the cytosol. This represents the first study of the cellular interactions of high-aspect ratio 1D metal nanomaterials and will facilitate the rational design of plasmonic nanoconstructs as cytosolic nanoagents for potential diagnosis and therapeutic applications.

Water transport facilitated by carbon nanotubes enables a hygroresponsive actuator with negative hydrotaxis.

Hygroresponsive actuators harness minor fluctuations in the ambient humidity to realize energy harvesting and conversion, thus they are of profound significance in the development of more energy-saving and sustainable systems. However, most of the existing hygroresponsive actuators are only adaptive to wet environments with limited moving directions and shape morphing modes. Therefore, it is highly imperative to develop a hygroresponsive actuator that works in both wet and dry environments. In this work, we present a bidirectional actuator responsive to both wet and dry stimuli. Our strategy relies on the introduction of carbon nanotubes to provide transport channels for water molecules. The actuation is enabled by the rapid transport of water in and out of the system driven by the moist/dry surroundings owing to the transport channels. The resultant actuator demonstrates reconfiguration and locomotion with turnover frequency F = 30 min-1, coupled with the capability of lifting objects 6 times heavier and transporting cargos 63 times heavier than itself. Oscillations (24°) driven by dry air flow in a cantilever display a high frequency (2 Hz) and large amplitude. Furthermore, a touchless electronic device was constructed to output varying signals in response to humid and dry environments. Our work provides valuable guidance and implications for designing and constructing hygroresponsive actuators, and paves the way for next-generation robust autonomous devices to exploit energy from natural resources.

Magnetic Janus nanocomposites with iridium(iii) complexes for heterogeneous catalysis of logic controlled RAFT polymerization using multiplexed external switching.

Photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization has emerged as a versatile and highly-efficient method for the polymerization of more activated monomers including N,N-dimethylacrylamide and methyl acrylate, and less activated monomers including N-vinylpyrrolidone and vinyl acetate, whilst imposing composition, sequence and spatiotemporal regulation. Although significant progress has been achieved in terms of ability to regulate PET-RAFT polymerization through the implementation of myriad environmental cues, it is still a great challenge to introduce multiple external switches within a single catalyst to accomplish logic toggling of controlled radical polymerization (CRP). Herein, we report the synthesis and characterization of Fe3O4@aSiO2@PNMIr Janus nanocomposites coupled with immobilized heteroleptic iridium(iii) complexes for heterogeneous catalysis of PET-RAFT polymerization. With this catalytic nanoarchitecture, we demonstrate multi-stimuli switching of CRPs using three different external physical manipulations: light "ON"/"OFF", magnet "OUT"/"IN" and temperature "LOW"/"HIGH". In addition, these magnetic Janus nanocomposites endowed radical polymerization with various attractive characteristics such as compatibility of myriad monomer formulations including "more activated" and "less activated" monomers, unique oxygen tolerance and ppm-level catalyst dosage. Logic-controlled polymerization with Fe3O4@aSiO2@PNMIr nanocomposites provides a straightforward, robust and user-friendly strategy for realizing multiplexed external switching of polymer propagation using a single nanocatalyst without the involvement of exogenous reagents.

A Smart Route for Encapsulating Pd Nanoparticles into a ZIF-8 Hollow Microsphere and Their Superior Catalytic Properties.

The encapsulation of catalytically active noble metal nanoparticles (NM NPs) into metal-organic frameworks (MOFs) represents an effective strategy for enhancing their catalytic performance. Despite a myriad of reports on the nanocomposites consisting of NM NPs and MOFs, it remains challenging to develop a sustainable and convenient method for realizing confined integration of NM NPs within a porous and hollow zinc-based MOF. Herein, a simple and well-designed approach is reported to the fabrication of Pd@ZIF-8 hollow microspheres with a number of Pd nanoparticles immobilized on the inner surface. This method capitalized on the use of polyvinylpyrrolidone (PVP)-stabilized polystyrene (PS) microspheres as templates, to harness the dual functions of PVP for reducing PdCl2 to generate Pd NPs and coordinating with zinc ions to grow ZIF-8 shells. Consequently, it avoids the complicated protocols involving surface treatment of template microspheres that conventionally adopts hazardous or costly agents. The obtained Pd@ZIF-8 hollow microspheres exhibit outstanding catalytic activity, size selectivity, and stability in the hydrogenation of alkenes. This study presents both the advances in the green synthesis and great potential of Pd@ZIF-8 hollow microspheres for catalytic applications.

Sub-Nanometer Thick Gold Nanosheets as Highly Efficient Catalysts.

2D metal nanomaterials offer exciting prospects in terms of their properties and functions. However, the ambient aqueous synthesis of atomically-thin, 2D metallic nanomaterials represents a significant challenge. Herein, freestanding and atomically-thin gold nanosheets with a thickness of only 0.47 nm (two atomic layers thick) are synthesized via a one-step aqueous approach at 20 °C, using methyl orange as a confining agent. Owing to the high surface-area-to-volume ratio, abundance of unsaturated atoms exposed on the surface and large interfacial areas arising from their ultrathin 2D nature, the as-prepared Au nanosheets demonstrate excellent catalysis performance in the model reaction of 4-nitrophenol reduction, and remarkable peroxidase-mimicking activity, which enables a highly sensitive colorimetric sensing of H2O2 with a detection limit of 0.11 × 10-6 m. This work represents the first fabrication of freestanding 2D gold with a sub-nanometer thickness, opens up an innovative pathway toward atomically-thin metal nanomaterials that can serve as model systems for inspiring fundamental advances in materials science, and holds potential across a wide region of applications.

Robust hollow nanocomposites with ruthenium-bipyridine complexes for heterogeneous catalysis of logic-controlled RAFT polymerization.

Photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization has become a powerful and eco-friendly toolkit to create well-defined macromolecular buildups while exhibiting composition, sequence and spatiotemporal control. Although PET-RAFT polymerization is generally much more convenient than living ionic polymerization, it is still a great challenge to regulate the polymerization upon multiple external stimuli and to simplify the procedures of post-polymerization purification. In this contribution, hHPGE-PFPPNRu nanocomposites were engineered as catalyst supports to firmly accommodate ruthenium-bipyridine complexes for heterogeneous catalysis of PET-RAFT polymerization. The manipulation of reaction temperature modulated the performance of the nanocatalysts, with a pronounced acceleration of the polymerization kinetics being identified at a temperature above the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM) brushes compared to that below it. Consequently, the control of RAFT polymerization can be achieved upon the dual-stimuli of light and heat. Moreover, these nanocatalysts conferred radical polymerizations with myriad attractive features such as the adaptability of diverse monomer formulations and reaction media, exquisite control over the molecular variables, oxygen tolerance, and catalyst doses in the ppm range. Owing to the robust mechanical nature of nanocomposites, the separation and reuse of the nanocatalysts were readily realized by rapid centrifugation, and they showed inappreciable catalyst leakage along with consistent catalytic performance even after multiple polymerization runs.

Buckled Amorphous Hollow Carbon Spheres: Facile Fabrication, Buckling Process, and Applications as Electrode Materials for Supercapacitors.

Buckled hollow carbon nanospheres (BHCSs) integrate several attractive properties desired for a variety of potential applications. However, the development of a feasible and simple method for preparing BHCS nanoparticles remains a great challenge. Herein, we present a facile strategy for fabricating monodisperse BHCSs via the compression of intact hollow carbon nanospheres (HCSs) with improved mechanical strength. The essence of our strategy lies in the successful preparation of robust HCSs that can sustain large mechanical deformation during compression, based on the introduction of polyvinylpyrrolidone in the synthesis of HCS templates. Both experiments and finite element analyses are conducted to probe the deformation mechanism of buckling, suggesting that the residual stress introduced by pyrolysis of precursors plays a predominant role in the buckling process. Furthermore, the use of BHCSs as high-performance supercapacitors is demonstrated. Our work provides important insights into the engineering of robust amorphous carbon nanomaterials by the template method and mechanical modulation and provides an innovative synthetic strategy for fabricating asymmetric hollow spheres with potential for a diversity of applications.

Optimising gold nanorods for photoacoustic imaging in vitro.

Gold nanorods (AuNRs) can be synthesised with different sizes but similar aspect ratios and therefore similar surface plasmon resonances (SPRs). Their strong optical absorbance governed by their SPRs facilitates their ability to be used as molecular-targeted contrast agents for photoacoustic (PA) imaging. The size of AuNRs has an effect on the PA conversion efficiency, melting threshold, and cytotoxicity, indicating that size can have a significant impact on overall biomedical efficacy. We investigated these factors for four different AuNRs (widths of 10, 25, 40 and 50 nm) all with SPRs of 815 ± 26 nm. A size-dependent linear relationship between fluence and PA amplitude was observed, along with particle melting. Reshaping was confirmed via transmission electron microscopy and spectrophotometry at a laser fluence of 11 ± 1.7 mJ cm-2, 20 ± 2.2 mJ cm-2, and 40 ± 2.6 mJ cm-2. Cytotoxicity was tested on lung cancer cells (A549) via a colourimetric assay at a maximum concentration of 3 × 1010 NP ml-1. Results demonstrate the 40 nm and 50 nm AuNRs produced the highest signal for equivalent particle numbers, but displayed the highest toxicity. Conversely, the 10 nm AuNRs were the most efficient photoacoustic converters, at equivalent total mass. This study demonstrates the importance of AuNR size and concentration on selection of AuNRs for their eventual clinical use.

Developing Hollow-Channel Gold Nanoflowers as Trimodal Intracellular Nanoprobes.

Gold nanoparticles-enabled intracellular surface-enhanced Raman spectroscopy (SERS) provides a sensitive and promising technique for single cell analysis. Compared with spherical gold nanoparticles, gold nanoflowers, i.e., flower-shaped gold nanostructures, can produce a stronger SERS signal. Current exploration of gold nanoflowers for intracellular SERS has been considerably limited by the difficulties in preparation, as well as background signal and cytotoxicity arising from the surfactant capping layer. Recently, we have developed a facile and surfactant-free method for fabricating hollow-channel gold nanoflowers (HAuNFs) with great single-particle SERS activity. In this paper, we investigate the cellular uptake and cytotoxicity of our HAuNFs using a RAW 264.7 macrophage cell line, and have observed effective cellular internalization and low cytotoxicity. We have further engineered our HAuNFs into SERS-active tags, and demonstrated the functionality of the obtained tags as trimodal nanoprobes for dark-field and fluorescence microscopy imaging, together with intracellular SERS.

Corrigendum: Morphological control of seedlessly-synthesized gold nanorods using binary surfactants (2018 Nanotechnology 29 135601).

Two errors have been found in paragraph 2 of section 2.2. An incorrect volume for the amount of AgNO3 solution added and the order in which solutions were added is wrong.

A bio-inspired homogeneous graphene oxide actuator driven by moisture gradients.

An actuator driven by moisture gradients has been developed from a homogeneous graphene oxide film, relying on the in situ formation of a bilayer structure induced by water adsorption. This actuator shows efficient and controllable bending motions, coupled with the capability of lifting objects 8 times heavier than itself.

Confined Assembly of Hollow Carbon Spheres in Carbonaceous Nanotube: A Spheres-in-Tube Carbon Nanostructure with Hierarchical Porosity for High-Performance Supercapacitor.

Carbonaceous nanotubes (CTs) represent one of the most popular and effective carbon electrode materials for supercapacitors, but the electrochemistry performance of CTs is largely limited by their relatively low specific surface area, insufficient usage of intratube cavity, low content of heteroatom, and poor porosity. An emerging strategy for circumventing these issues is to design novel porous CT-based nanostructures. Herein, a spheres-in-tube nanostructure with hierarchical porosity is successfully engineered, by encapsulating heteroatom-doping hollow carbon spheres into one carbonaceous nanotube (HCSs@CT). This intriguing nanoarchitecture integrates the merits of large specific surface area, good porosity, and high content of heteroatoms, which synergistically facilitates the transportation and exchange of ions and electrons. Accordingly, the as-prepared HCSs@CTs possess outstanding performances as electrode materials of supercapacitors, including superior capacitance to that of CTs, HCSs, and their mixtures, coupled with excellent cycling life, demonstrating great potential for applications in energy storage.

Morphological control of seedlessly-synthesized gold nanorods using binary surfactants.

High purity gold nanorods (AuNRs) with tunable morphology have been synthesized through a binary-surfactant seedless method, which enables the formation of monocrystalline AuNRs with diameters between 7 and 35 nm. The protocol has high shape yield and monodispersity, demonstrating good reproducibility and scalability allowing synthesis of batches 0.5 l in volume. Morphological control has been achieved through the adjustment of the molar concentrations of cetyltrimethylammonium bromide and sodium oleate in the growth solution, providing fine tuning of the optical scattering and absorbance properties of the AuNRs across the visible and NIR spectrum. Sodium oleate was found to provide greatest control over the aspect ratio (and hence optical properties) with concentration changes between 10 and 23 mM leading to variation in the aspect ratio between 2.8 and 4.8. Changes in the geometry of the end-caps were also observed as a result of manipulating the two surfactant concentrations.

One-step fabrication of hollow-channel gold nanoflowers with excellent catalytic performance and large single-particle SERS activity.

Hollow metallic nanostructures have shown potential in various applications including catalysis, drug delivery and phototherapy, owing to their large surface areas, reduced net density, and unique optical properties. In this study, novel hollow gold nanoflowers (HAuNFs) consisting of an open hollow channel in the center and multiple branches/tips on the outer surface are fabricated for the first time, via a facile one-step synthesis using an auto-degradable nanofiber as a bifunctional template. The one-dimensional (1D) nanofiber acts as both a threading template as well as a promoter of the anisotropic growth of the gold crystal, the combination of which leads to the formation of HAuNFs with a hollow channel and nanospikes. The synergy of favorable structural/surface features, including sharp edges, open cavity and high-index facets, provides our HAuNFs with excellent catalytic performance (activity and cycling stability) coupled with large single-particle SERS activity (including ∼30 times of activity in ethanol electro-oxidation and ∼40 times of single-particle SERS intensity, benchmarked against similar-sized solid gold nanospheres with smooth surfaces, as well as retaining 86.7% of the initial catalytic activity after 500 cycles in ethanol electro-oxidation). This innovative synthesis gives a nanostructure of the geometry distinct from the template and is extendable to fabricating other systems for example, hollow-channel silver nanoflowers (HAgNFs). It thus provides an insight into the design of hollow nanostructures via template methods, and offers a versatile synthetic strategy for diverse metal nanomaterials suited for a broad range of applications.

Dual lanthanide role in the designed synthesis of hollow metal coordination (Prussian Blue analogue) nanocages with large internal cavity and mesoporous cage.

Prussian Blue (PB) analogue metal coordination nanocages comprised of mesoporous walls (ca. 3.5 nm pore width) encapsulating a cavity approaching ca. 100 nm in diameter (surfactant free) are presented as an advance in rational metal coordination polymer nanostructure design. The synthesis employs lanthanide ions (Gd(3+) or Er(3+)) which function initially as peripheral coordination crosslinkers of metallo-surfactant templated miniemulsion droplets, and, subsequently, as promoters in the removal of the organic component of those surfactants via metal-assisted ester hydrolysis. The success of this synthetic strategy relies entirely on the periphery coordination event occurring prior to the ester hydrolysis surfactant removal step. Crucially, this one-pot sequential synthesis was achieved using a newly developed metallo-surfactant designed to have a reduced ester hydrolysis rate. Syntheses of this innovative metallo-surfactant, intermediary PB analogue coordination polymer organo-nanoshells and the subsequent conversion to hollow metal coordination nanocages are fully characterised using a wide variety of techniques, including TEM, SEM, EFTEM, EDX, TGA, WAXD, NMR, N(2) adsorption, etc., and represent the first designed synthesis of hollow metal coordination nanocages containing a large nanoscale cavity (wall of hollow nanosphere is mesoporous; hence nanocage).

Photoluminescent properties of Prussian Blue (PB) nanoshells and polypyrrole (PPy)/PB core/shell nanoparticles prepared via miniemulsion (periphery) polymerization.

We fabricated PPy/PB core/shell nanoparticles via one-step miniemulsion polymerization using a metallosurfactant of EPE-Fe. The defined hollow structure endows PB nanoshells with an emission band at 612 nm. On incorporating PPy inside PB shells, a blue shift and enhanced fluorescence were observed due to charge transfer from PPy to PB.

pH-responsive luminescent properties of Ag@PPy nanoparticles.

We measure the emission spectra and quantum yields of Ag@PPy nanoparticles with different volume ratios of Ag core and PPy shell, and ascribe the emission peaks around 460 and 520 nm, respectively, to the S(1) → S(0) transition of the PPy molecule, and to the charge transfer between Ag and PPy, as well as the Ag plasmon. The two peaks shift with the changed doping level of the PPy shell, which can be elucidated by consideration of the energy levels of Ag and PPy. According to these results, we investigate the fast and reversible pH-sensing function of Ag@PPy nanoparticles on the basis of the doping effect on the interaction between the Ag core and the PPy shell.

Contribution of charge-transfer effect to surface-enhanced IR for Ag@PPy nanoparticles.

A unique surface-enhanced infrared absorption phenomenon was found and investigated for Ag@polypyrrole nanoparticles. Enhancement of the peak at 1384 cm(-1), corresponding to a C-H bending vibration, gave information on the orientation of the polypyrrole (PPy) molecule in Ag@PPy nanoparticles. It was observed that the contribution of the charge-transfer effect can be amplified with an increased quantity of oxidant FeCl(3) in the polymerization of pyrrole on the Ag core, suggesting that the doped Cl(-) ions in the conductive PPy shell may bring an alteration of the local Fermi level of the Ag nanoparticles and the energy levels in the PPy moleclue, thus achieving an optimal energy matching. These results demonstrated the potential of Ag@PPy nanoparticles as photonics and electronics devices and opened out the applicability of the SEIRA in more-interesting and practical systems.